A charge plate monitor includes a measuring instrument main body, a display device composed of a seven-segment display or a liquid crystal display, a measurement plate connected to the measuring instrument main body, a bar type ionizer which is a subject to be evaluated for performance, and a plurality of emitters (discharge electrodes) arranged in a longitudinal direction of the ionizer. The measuring instrument main body includes a high voltage power supply or an electro static voltmeter, an electric field meter, a timer, etc. The measuring instrument main body has a primary function of measuring a surface potential of the measurement plate, and also measures a static elimination performance and an ion balance performance of the ionizer. The measurement plate is structured such that two conductive plates having a size of 150 mm in each side are spaced from each other with a gap of 6 to 20 mm therebetween and combined with each other. The measurement plate has an overall capacity of about 20 pF.
First, to evaluate the static elimination performance of the ionizer, a high voltage of, for example, +1000 V or −1000 V needs to be applied to the measuring instrument main body for electrical charging, thereby causing ions generated by the ionizer to reach the measurement plate. In this state, charges in the measurement plate are neutralized by negative ions. A time taken for a voltage to drop from +1000 V to +100 V, or from −1000 V to −100 V (attributable to neutralization by positive ions) is measured by the measuring instrument main body. The shorter the time, the larger amount of ions the ionizer generates. Therefore, when the time is short, it is considered that a static elimination performance is high. There are various types of measurement plates classified according to voltages, i.e. from ±1000 V to ±5000 V, applied thereto. A mode in which this measurement operation is performed is called attenuation measurement mode.
Second, to evaluate an ion balance performance, the measurement plate is grounded to a voltage of 0 V. This causes positive and negative ions generated by the ionizer to reach the measurement plate. In this case, when the amount of positive ions and the amount of negative ions generated by the ionizer become equal to each other, the electrical potential of the measurement plate becomes stable at about a voltage of 0 V. At this point, the magnitude and polarity of the electrical potential are measured by the measuring instrument main body to evaluate the ion balance performance of the ionizer. A mode in which this measurement operation is performed is called ion balance measurement mode.
There is a trend that a substrate for a liquid crystal display or a plasma display, from which charges need to be removed, is increased. Accordingly, the length of a bar type ionizer correspondingly increases. When evaluating performance of a long-size ionizer by using a single charge plate monitor, it is necessary to measure the performance while moving the single charge plate monitor in a lengthwise direction of the ionizer because a plurality of emitters is arranged over a range of the full length of the ionizer in the lengthwise direction. For this reason, it takes much labor and time to evaluate performance of even a single ionizer. To solve this problem, a plurality of charge plate monitors may be used. In this case, it is possible to evaluate the performance of a long-size ionizer by performing a measurement operation only one time. However, this method incurs high costs because the charge plate monitors are expensive.
Japanese Patent Application Publication No. 10-2008-519260 (published as of Jun. 5, 2008.06.05) discloses an ion balance monitor in which a measurement plate is divided into a plurality of sections and the sections are applied with different bias voltages, thereby simultaneously measuring an ion balance performance and an ion generation rate. According to this disclosure, the measurement plate is divided into a plurality of sections, and the alternate sections are applied with a plus bias voltage and a minus bias voltage, respectively. The measurement plate measures an ion balance state or an ion generation rate of positive and negative ions generated by an ionizer. However, the disclosed technology cannot solve the problems of a laborious measurement operation and a long measurement time attributable to the long length of the ionizer.
Korean Patent Application Publication No. 10-2012-0049780 (published as of May 17, 2012) discloses a charge plate monitor for measuring a static elimination performance or an ion balance performance (performance of maintaining balance between positive ions and negative ions) to evaluate the performance of an ionizer. The charge plate monitor detects positive and negative ions generated by the ionizer using a measurement plate, and evaluates balance between positive and negative ions. In the charge plate monitor, a single measuring instrument main body is provided with two functions: reducing a time taken for a preliminarily applied electrical potential of the measurement plate to be attenuated to a predetermined electrical potential by generated ions; and measuring an ion balance performance on the basis of the electrical potential of the measurement plate. According to this technology, a plurality of measurement plates is prepared. The number of measurement plates used is determined depending on the length of an ionizer to be evaluated for performance thereof. The measurement plates are connected to the measuring instrument main body in series or in parallel. According to the disclosed technology, a number of measurement plates, the number of which corresponds to the number of required tables, are connected to a single measuring instrument main body in series or in parallel. Therefore, it is possible to evaluate a static elimination performance and an ion balance performance of a long ionizer using only a single charge plate monitor, thereby resulting in reduction in time and costs for performance evaluation of the ionizer. In addition, this technology can be applied to various ionizers having different lengths by changing the number of tables of the measurement plates connected to the measuring instrument main body in accordance with the length of the ionizer.
As illustrated in FIG. 1, the measurement plate of the conventional charge plate monitor includes a conductive plate,
a floating ground that is separated from an earth ground, and an insulator provided between the conductive plate and the floating ground.
For measurement, an equivalent capacitance (for example, capacitance of 20 pF±2 pF) needs to be formed in the measurement plate by using a voltage follower separating the conductive plate and the floating ground from each other. In the case of contact type measurement, since it is necessary to apply a high voltage of 1000 V to the floating ground while following (tracing) an input voltage that is input to the conductive plate, a high voltage cable is required. Therefore, this case has a disadvantage that selection of a high voltage cable is critically important. In the case of noncontact type measurement, when a high voltage is applied, mechanical connection and subsequent perfect separation need to be performed. This case has a disadvantage that a mechanical device influencing the weight and size of the conventional charge plate monitor needs to be used.